Carver TFM-22 offset, and distorted

Archived from groups: rec.audio.tech (More info?)

Hi folks,

I have two TFM-22's with identical problem. The right channel is offset
at about -.3 volts at the speaker terminal with or without speaker
connected, the amp has terrible zero crossing distortion, and shuts down
if played above about 1/2 watt output. The outputs are underbiased in this
failure mode, as the heatsink never gets warm on the bad side.

Here is a weird thing, I swapped CN101, and CN102, the drive from the
input board, and the problem remained on the right side, indicating a
problem in the high power section. I returned CN101, and CN102 to their
proper place, and the amp plays fine. What the heck???? I did not try
this on the other amp, as I am sure I haven't really fixed anything yet.

Anyone ever have this problem? What would you think? A transistor with
leakage that was somehow cleared when I was swapping drive signals? (Yes,
the power was off, but the caps were still about 1/2 charged, and yes, that
was a dumb thing to do, could have toasted the whole thing)

Archived from groups: rec.audio.tech (More info?)

In article <3gqn2jFdm540U2@uni-berlin.de>, jana@ca.inter.net says...
>
>There are many factors that can cause this fault. Basically, the amp would
>need proper troubleshooting on the bench to determine the components that
>are off value. Because of the critical nature of the design of an audio
>output stage, a component that is slightly off value can cause this type of
>fault. When components are failing, there is also a chance of having some
>unstable conditions.
>
>To troubleshoot your amp, it would require the proper test tools, service
>manual, and a lot of experience. These high end amplifiers are a bit complex
>to work on. After servicing, it would be ideal to do all the tests including
>a distortion test.
>
>If you would like your amp properly service, it would be best to contact the
>manufacture directly, and have them direct you to their authorized service
>rep for your area.
>
>--
>
>JANA
>_____
>

I have all the tools, including distortion analysers, signal generators,
tektronix o'scope, etc. etc., I am a broadcast engineer, maintaining two
fm's, and one am, also been an advanced class ham operator for over 10
years. It is not the lack of equipment or knowledge that I suffer. It is
that I was looking for someone with a similar experience with Carver TFM's.

The fact that these two amps have an identical symptom tells me it may
perhaps be a common problem. Funny no one suggested gluing heat sinks on
to the pair of pre-drivers, and the pair of drivers that have scorched the
circuit board. Every Carver TFM I ever had open showed this overheat symptom
in the pre-drive section, and I have been gluing heat sinks on, and adding
fans to every TFM 25 or bigger, that I ever put into a commercial sound
installation. Never had one fail after adding fans. Had one fail when some
numbnuts disconnected my fans however.

High end? Matter of opinion. Complex, hardly, Carver TFM's are very
simple and straight forward in design. Quasi comp-sym basically. Every
component exactly where I would expect it to be, and for the reason it
should be there. Complex is the ships radars I service every day as a
side line to being a full time engineer.

BTW, JANA, is that an abrieviation, or is that Skandik nafn?
Eg er Gudmundur, Hestamaðurinn fra Hvollsvollir hja við Hella a Islandi.